Calorimetry in Materials

#### **Chapter 4**

## Comparative Study of Setting Time and Heat of Hydration Development of Portland Cement According to EN 196-3

*Katalin Kopecskó and Attila Baranyi*

### **Abstract**

One of the most critical properties of cementitious materials is the initial (IST) and final (FST) setting time, which helps to plan the transportability, workability and demoulding of concrete over time. The standards used to determine the setting time are based on measurement of penetration resistance; these are measured of the depth of penetration with a well-defined body (usually a Vicat needle) into a cement paste as a function of time. Two European standards deal with setting time: EN-196-3 and EN 480-2. EN 196-3 is used to determine the setting time of cement paste of standard consistency. Semi-adiabatic calorimetry (SAC) can be a suitable method for determining the setting time of cementitious materials and concretes of non-standard consistency. This method examines the heat evolution of the hydration reaction of cement. The heat evolution is proportional to the change in viscosity during the setting process and to the Vicat needle penetration depth. This study aimed to find a simple, more accurate and cheaper alternative measurement method for determining the setting time of cementitious materials, which can also be applied to concretes.

**Keywords:** Portland cement, setting time, IST, FST, semi-adiabatic calorimetry, SAC, EN-196-3

#### **1. Introduction**

One of the most important parameters of the cementitious materials is the initial (IST) and final (FST) setting time. Knowing these data, it is possible to plan the maximum workability, casting (IST), and the initial hardening time can be estimated (FST) for formwork removal. The hydrate compounds formed during the hydration of clinker minerals (alite, belit, celite, felite) that evolve a solid matrix from the viscous slurry. The standards used currently measure this

transformation process using various penetration resistance procedures (ASTM C191–19, ASTM C266–20, ASTM C403/C403M-16, ASTM C807–20, ASTM C953–17, AASHTO T131–20, AASHTO T154–18, ISO 9597:2008). These technics can be for example the Vicat needle test, Gillmore needles test, and the Hilti nail gun test [1].

The most common method for setting time measurement is the Vicat needle test. This method is applied by EN 196–3. A needle of well-defined weight and diameter is penetrated into cement paste of standard consistency during the process. The penetration of the needle is inversely proportional to the actual viscosity of the test sample, thus and the setting progress.

Despite the simplicity and prevalence of this method, several attempts have been made to induce the penetration method as this technique is applicable only for cement sludge and does not allow monitoring of the whole cement setting process. Such a method includes measuring ultrasonic impulse velocity [2–6] and the electrical resistance [7–9]. These methods are complex in structure and require high-level expertise that makes their use difficult.

Recently, the measurement based on semi-adiabatic calorimetry (SAC) has become popular for determining the setting time of cementitious materials [10–18]. During the procedure, the change in the hydration heat development of the cement is monitored as the clinker minerals chemically react with the water, which results in heat generation (exothermic reaction). The resulting temperature change usually follows the change in mechanical properties as well. The advantage of thermal analysis is the simple design of the measuring system which consists only of a thermally insulated vessel (calorimeter), a thermocouple and a data logger. In addition, ASTM C1679 and ASTM C1753 can help design and improve the successful execution of SAC tests.

During our measurement, we observed several disadvantages of the Vicat method prescribed by the EN 196–3 standard: discontinuous, inaccurate method, the drop number is limited, the examination of non-standard consistency (slightly plastic) mixtures is difficult. The standard measurement of the end of the setting time can be challenging with an automatic device, especially in the case of cementitious pastes with a long setting time [19–21], and automated devices are expensive equipment.

In this study, we compared the setting time of CEM I 42.5 N pure Portland cement according to EN 196–3 with the heat evaluation profile recorded during the calorimetric tests with three different water/cement (w/c) ratios. The measured cement paste was prepared using only deionised water and cement; no admixtures were added for the mixture preparation.

According to our hypothesis, the Vicat method can be substitute heat hydration measurement of the cement paste based on the results obtained from the synchronising of the two processes.

#### **2. Short introduction of EN 196-3 standard**

Currently, there are two European standards in force for determining the setting time of cementitious materials. The EN 196–3 cement testing method and the EN 480– 2 deal with investigating concrete admixtures, but this standard also uses the Vicat method.

The same method is used for ASTM standards. These methods also measure the penetration resistance during the setting of cementitious materials using the Vicat and *Comparative Study of Setting Time and Heat of Hydration Development of Portland Cement… DOI: http://dx.doi.org/10.5772/intechopen.101912*

the Gillmore method. However, these standards already include mortar and concrete testing (ASTM C403/C403M-16, ASTM C807–20, ASTM C953–17).

The EN 196–3 standard principle is *"cement paste of standard consistency has a specified resistance to penetration by a standard plunger."* The water content of the cement paste of standard consistency must be determined from several different mixtures. The setting time is defined by *"observing the penetration of a needle into cement paste of standard consistency until it reaches a specified value."*

The standard specifies the following parameters:

	- the cement and water must be added within 10 s (zero time),
	- start mixing at slow speed (140 5 rpm) for 90 s,
	- the mixing must be stopped for 30 s during this time the cement paste must be scraped off the wall of the bowl and placed in the middle of it,
	- it follows another 90 s mixing, so the whole mixing time is 30 min.
	- Plunger for determination of standard consistency: cylinder of at least 45 mm effective length and of (10.00 0.05) mm diameter (**Figure 1**).
	- Vicat needle for initial set: steel and in the form of a right cylinder of effective length of at least 45 mm and diameter (1.13 0.05) mm (**Figure 1**).
	- The total mass of moving parts shall be (300 1) g.
	- Needle with attachment for final set: a needle with a ring attachment of diameter approximately 5 mm (**Figure 1**)
	- Vicat mould: it shall be made of hard rubber, plastics or brass. It shall be of cylindrical or truncated conical form (40.0 0.2) mm deep and shall have an internal diameter of (75 10) mm. A base plate must be placed which is larger than a ring and at least 2.5 mm thick, waterproof and resists to the effect of cement paste.

#### **Figure 1.**

*Plunger for determination of standard consistency (left) Vicat needle for initial set time determination (middle), needle with attachment for final set time evaluation (right) (EN 196–3).*

The cement paste must be prepared with a standard mixer according to the method as described in the EN 196–1. Then the lightly oiled Vicat mould is placed at a lightly oiled base plate (usually glass), then filled it with cement paste without compaction or vibration. The standard consistency of cement paste with smoothed upper surfaced is measured; then the plunger is changed for a needle at least 45 mm length and 1.13 0.05 mm in diameter, and the initial setting time for this water content is determined.

For initial setting time (IST), the standard refers to the time that elapses between the mixing of the cement paste (zero time) and the time until the distance between the needle and the base plate is 6 3 mm (penetration 34 3 mm). To determine the final setting time (FST), the mould should be inverted, and the measurement must be continued with the needle with attachment. The time when the needle is already less than 0.5 mm penetrated in the cement paste is considered to be the final setting time, so only the needle and not the attachment leaves a mark on the surface of the specimen.

#### **3. The problems during the standard measurement**

The Vicat method, according to EN 196–3 is a penetration measurement, which can only be applied to standard consistency cement paste. It is possible to measure mortar with a modified Vicat test recommended by ASTM C807, but this method cannot be used for mortars with non-standard consistency. For the determination of setting time of concretes, an approximate result can be obtained by penetration resistance measurement using ASTM C403.

The method recommended by EN 196–3 can be challenging to determine for mixtures with non-standard consistency (viscosity). The Vicat mould can easily tip over, and the lower viscosity materials may leak at the bottom of the ring. Therefore, we designed a threaded Vicat mould (**Figure 2**) that also includes the base plate and fits precisely on the rotating plate of the Controls Vicamatic2 instrument used in our studies.

*Comparative Study of Setting Time and Heat of Hydration Development of Portland Cement… DOI: http://dx.doi.org/10.5772/intechopen.101912*

**Figure 2.** *Threaded Vicat mould.*

After determining the IST, the threaded Vicat mould can be disassembled as needed and then inverted with the cement paste placed in it to measure FST. However, in the case of measurements with automatic Vicat instrument, it is impossible or very complicated to determine the end of the setting time according to the standard. Thus, the needle for the initial set is most often used for the whole test, and the sample is usually not reversed. In this case the shrinkage of the specimen must be considered by the effect of which FST seemingly appears at penetration rate more than 0.5 mm in the case of most measurements.

One of the main disadvantages of this method is from its discontinuous nature, due to which we cannot monitor the binding process precisely. The penetration resistance of cement paste which is proportional to changes in the viscosity of the material can be estimated by only individual "sampling".

The automatic device we use can perform 44 standard drops, which means that when measuring mixtures with unknown setting times, this "sampling" has to be managed, especially in the case of cement pastes with a long setting time [19–21]. We can miss the IST if we start the measurement too early or set up a too-long delay time on the automatic Vicat device. In addition, care must be taken to set the proper drop sequence in order to achieve sufficient measurement accuracy.

#### **4. Determination of setting time by thermal method**

In order to avoid the problems mentioned above and to be able to monitor the setting process, semi-adiabatic calorimetry (SAC) is an increasingly widespread method for determining the setting time of cementitious mixtures [10–18].

The SAC method is suitable for determining the setting time of cement paste, mortar, and concrete, respectively. We can monitor the setting process; it is possible to measure more accurately. It is not disturbed by the shrinkage of the specimen. It can be done with a simpler and cheaper measuring instrument.

The ASTM C403 standard proposes two methods for the thermal determination of the setting time:

• The **Derivatives method** determines the initial setting time (IST), as the time which results from the maximum curvature of the second derivative of the hydration temperature–time function (**Figure 3**). It defines the final setting time (FST), as the time corresponding to the peak of the first derivative curve of the

**Figure 3.** *Determination of IST from the derivatives method.*

**Figure 4.** *Determination of FST by the derivatives method.*

temperature–time function (**Figure 4**). This method may function well for clear data sets, but it is sensitive to the peaks not belonging to the ones occurring in data and to environmental changes [10, 11, 14, 15, 18].

• The **Fractions method** defines the initial and final setting times as a percentage of the temperature rise below the main hydration peak from baseline to the measured maximum (**Figure 5**). The initial and final setting times are determined as a percentage of the total semi-adiabatic temperature rise of the sample. 21% and 42% are the default initial and final setting time values at standard laboratory curing conditions [10, 11, 14, 18].

This method is more stable than the Derivatives method, but it is more sensitive to the definition of baseline temperature [10].

*Comparative Study of Setting Time and Heat of Hydration Development of Portland Cement… DOI: http://dx.doi.org/10.5772/intechopen.101912*

**Figure 5.** *Determination of the IST and FST as defined by fractions method.*

#### **5. The comparative measurement heat of hydration and the setting time according to EN 196-3**

In our work, we investigated whether there is a simple correlation between the standard Vicat method and the heat evolution measurement results similar to the ASTM standard methods, which could lead to a method based on in many respects cumbersome and inaccurate penetration measurements. The tests were performed using CEM I 42.5 N cement and deionised water at 0.25, 0.28 and 0.31 water/cement ratios (w/c) at 26 0.5°C. For the measurement we used Controls Vicamatic2 type automatic Vicat device, 300x400x300 mm polystyrene calorimeter and Comet M1200 data logger. We made three parallel measurements from each w/c; then the results were averaged.

In the first step, we synchronised the clock of the Vicat device and the data logger, and then we prepared the cement paste with the given w/c ratio according to the standard. For mixing, a standard Controls 65-L0502 mortar mixer was used to prepare a sufficient amount of sample for both Vicat and heat evolution testing.

For the standard setting time measurement, the threaded Vicat mould (**Figure 2**) was filled with cement paste and placed on the rotating plate of the automatic Vicat device. Air bubbles were removed from the sample by gentle tapping, and then the surface was smoothed.

For the semi-adiabatic (SAC) measurement, 1800 g (about 1 dm<sup>3</sup> ) of the same cement paste was filled into a 1 l beaker pre-smeared with a form release agent. The sample was placed in the calorimeter. The Teflon-coated thermocouple was then immersed so that it extended to the centre of the sample (**Figure 6**).

During the measurement of heat of hydration the frequency of the temperature data collection was 5 min. By increasing the w/c, the Vicat measurement had to be started with a delay because the binding started later due to the higher water content.

**Figure 6.** *Polystyrene calorimeter with data logger.*

#### **6. Results and discussion**

Data from the standard Vicat method and heat evolution measurements were synchronised and plotted on one graph (**Figures 7**–**9**). We represented the depth of each penetration of Vicat measurement on bar graphs in the setting time – heat development diagrams, while the blue curve shows the hydration heat development of the cement. The penetration at IST is marked with a blue bar; and the FST is marked with a red column according to EN 196–3 standard.

According to the standard, when the penetration depth of the needle sinks only 34 3 mm (6 3 mm from the base plate) into the test specimen is considered to be IST. Thus, the time corresponding to the penetration depths of 37 and 31 mm can also be considered IST, which means that it is up to the person performing the measurement to consider which time he considers the initial setting time. This method can cause a problem, especially when measuring mixtures with long setting times, where this interval can mean a difference of several hours [19–21]. Determining the end of the setting time is even more of a problem, as penetration damages the surface of the specimen during the test and lowers it due to possible shrinkage, which makes it difficult to determine the FST accurately.

**Figure 7.** *Setting time—Heat evolution function (left), derivative method (right), w/c = 0.25.*

*Comparative Study of Setting Time and Heat of Hydration Development of Portland Cement… DOI: http://dx.doi.org/10.5772/intechopen.101912*

**Figure 8.** *Setting time—Heat evolution function (left), derivative method (right), w/c = 0.28.*

#### **Figure 9.**

*Setting time—Heat evolution function (left), derivative method (right), w/c = 0.31.*

We considered the initial setting time to be the first penetration values smaller than 37.00 mm during our measurements. However, in determining the FST, we compared the previous test performed according to the standard (needle exchange, inversion of the specimen) with the result of the test performed with the needle used for the initial set, without inverting the specimen. Based on these, the time of penetration less than 2.00 mm below the level previously calibrated to 40 mm was considered to be the final setting time.

During the cement paste preparation previously, the temperature suddenly rises, then after a dormancy period, the temperature starts to rise again. In the case of the cement paste tested in the calorimeter, the maximum temperature exceeded 100°C in all cases. It was found that by increasing the w/c factor, the setting time is also extended in proportion to the initial temperature: w/c = 0.25 IST = 1:35–1:50, w/c = 0.28 IST = 2:05–2:15, w/c = 0.31 IST = 2:35–2:45 (see **Table 1**). Slower hydration is likely caused by an increased distance between particles [22]. Another factor may be that more water absorbs more heat, which is not used to accelerate the binding reaction.

At 0.25 w/c ratio, the initial setting time occurred at a temperature rise of 8.3–8.7°C, while at 0.31 w/c ratio, an initial temperature (26 0.5°C) of up to 10.5°C (**Table 1**). However, the temperature fluctuation of the mixtures prepared with the same w/c ratio measured at IST remained below 0.3°C, therefore the IST and FST values can be determined by measuring the temperature difference (ΔTIST, ΔTFST) similarly to the Fractions method at the same conditions. During our measurements, the initial setting


#### **Table 1.**

*Results of comparative measurements of Vicat and SAC method.*

time occurred at w/c = 0.25 is approx. 8.5°C, at w/c = 0.28 is approx. 9.0°C, and at w/ c = 0.31 approx. 10°C temperature rise.

Notations: Vicat—setting time values obtained by the Vicat method, SAC—results of semi-adiabatic calorimetry, Vicat-SAC—temperature values for setting times measured with Vicat needle.

We examined the applicability of the Derivative method, but as shown in **Figures 7**–**9**, we observed significant differences in the measurement results. Using the Derivative method, IST was 1:40–2:00 delayed compared to the Vicat method, irrespective of w/c, while FST followed it with a 5–10 min lag. Thus, FST occurred with a delay of 0:35 and 1:20 compared to the standard method after the measurement.

**Table 1** summarises the measurement results of the Vicat method and heat evolution. IST and FST denote the initial and final setting time, TIST, TFST mark the temperature value measured at this time, and ΔTIST and ΔT FST are the temperature difference measured from the initial temperature (26 � 0.5°C). The Tmax. and ΔTmax. are the maximum temperature or the corresponding temperature difference, while ΔtTmax. shows the spent time until the maximum temperature value is reached.

We also found similar differences in the Derivatives method with the Fractions method. **Table 2** shows the temperature values (TFract IST, TFract FST) for the given w/c ratio, calculated by the Fractional method, and the corresponding FSTs (Fract IST, Fract FST), and the difference between the results of the Fractions and the Vicat method (ΔtFract-IST, ΔtFract-FST) are indicated.

It can be seen that the IST values calculated by the Fractions method give on average 40–65 min longer and the FST 31–56 min longer set values. The proportional factors (kIST, kFST) calculated by us in relation to the setting time measured by the Vicat method, as a function of the w/c ratio, are summarised in **Table 3** (Eq. (1)). It was found that the constant proportionality factors of 21% and 42% given for the Fractions method increase with the w/c ratio.

$$k\_{ST} \,\left[\%\right] = \frac{\Delta T\_{ST}}{\Delta T\_B} \cdot 100\,\tag{1}$$

*Comparative Study of Setting Time and Heat of Hydration Development of Portland Cement… DOI: http://dx.doi.org/10.5772/intechopen.101912*


#### **Table 2.**

*Results of comparative measurements of Vicat and fractions method.*


#### **Table 3.**

*The calculated proportional factors compared with the Vicat values.*

where ΔTST is the temperature change belonging to IST or FST; ΔTB is the difference between the maximum and the initial (room) temperature.

Based on these results the setting times can be calculated as follows (Eqs. (2) and (3)):

$$
\Delta \mathbf{T}\_{\text{IST}} \text{ (IST)} = \mathbf{k}\_{\text{IST}} \left( \mathbf{w} / \mathbf{c} \right) \bullet \Delta \mathbf{T}\_{\text{B}}, \tag{2}
$$


**Table 4.**

*The differences between the time of maximum temperature and Vicat values.*

$$
\Delta \mathbf{T\_{FST}} \text{ (FST)} = \mathbf{k\_{FST}} \text{ (w/c)} \bullet \Delta \mathbf{T\_B} \tag{3}
$$

In our experiments, we assumed that for a given type of cement, with a defined w/c factor, for a given initial temperature and preparation method (see EN 196–3), the heat of reaction (heat of hydration) is the same under semi-adiabatic conditions. This also means that the reaction rate is constant, so the ratio of the time to maximum temperature (ΔtTmax.) and the setting times (IST, FST) do not change. So, we calculated these differences (Eq. (4)):

$$
\Delta \mathbf{t}\_{\text{Tmax}-\text{IST}} = \Delta \mathbf{t}\_{\text{Tmax.}} - \text{IST}; \Delta \mathbf{t}\_{\text{Tmax}-\text{FST}} = \Delta \mathbf{t}\_{\text{Tmax.}} - \text{FST} \tag{4}
$$

, which proved to be nearly constant as expected. The fluctuations in the results were largely due to an error in the Vicat method (**Table 4**).

#### **7. Conclusions**

The Vicat method prescribed by the EN-196-3 standard is a widespread measurement that is still in use today mainly due to its simple implementation. The measurement is used to determine the setting time of standard consistency cement paste; however, it is not suitable for non-standard flow cement paste or for testing mortars and concretes. It does not give a comprehensive picture of the setting process; it is inaccurate, which is a problem, especially in the case of cement pastes with a longer setting time. The measurement result depends to a large extent on the skill of the person performing the measurement, and in the case of the use of automatic Vicat devices, the end of the setting time cannot be determined according to the standard, or only with a great difficulty.

The semi-adiabatic calorimetric (SAC) method measures the amount of heat (reaction heat) released during the hydration reaction of a cementitious material, which is proportional to the reaction rate of the clinker minerals (and additives), i.e. the hardening process. The heat of hydration depends on the fineness of the grinding fineness of the cement, the w/c ratio, the method of preparation, the ambient temperature, the quality and quantity of additional materials. This means that for a given cement type and w/c ratio, at a constant environmental temperature, with the same mixing mode, the hydration heat development process takes place in the same way. Thus, for a given mixture, the time to the initial and final setting times and to the maximum of heat evolution is almost constant.

During our measurements, the setting properties of CEM I 42.5 N cement were investigated at 0.25, 0.28, and 0.31 w/c ratios with deionised water without admixtures and aggregates. We sought a parameter comparing the results of the heat evolution curve and the Vicat penetration test to estimate the initial (IST) and final (FST) setting time. As w/c increases, the setting time (ST) values extend and the associated temperature changes also increase, so these characteristics can only be used to determine the setting time for the mixtures of the same composition (Eqs. (5)–(7)).

$$\mathbf{w}/\mathbf{c} = \mathbf{0}.25 \qquad \text{IST} \propto \text{T}\_0 + \mathbf{8.5}^{\circ}\text{C} \tag{5}$$

w*=*c ¼ 0*:*28 IST∝T0 þ 9*:*0°C (6)

$$\mathbf{w}/\mathbf{c} = \mathbf{0}.\mathbf{31} \qquad \text{IST} \propto \text{T}\_0 + \mathbf{10}.\text{0°C} \tag{7}$$

where T0 is the initial temperature.

*Comparative Study of Setting Time and Heat of Hydration Development of Portland Cement… DOI: http://dx.doi.org/10.5772/intechopen.101912*

The IST, FST and the time to maximum temperature (ΔtTmax.) occur proportionally later for mixtures with higher w/c ratios, however, the time between them (Δt-Tmax-IST, ΔtTmax-FST) is almost constant (**Table 3**).

For the mixtures used in our studies, the IST and FST were measured 3.5 and 2.5 hours before ΔtTmax. Minor fluctuations were observed only in the determination of FST values caused by the uncertainty resulting from the Vicat method. We can conclude that the setting time (ST) of the cement paste made of ordinary Portland cement without admixtures and aggregates can be determined without the use of Vicat apparatus. It can be determined accurately by SAC method with the knowledge of the time to maximum temperature (ΔtTmax) corresponding to the maximum temperature value (Tmax.) (Eqs. (8) and (9)):

$$\text{IST} \propto \Delta \text{t}\_{\text{Tmax}} - \text{ $\mathfrak{J} : \mathfrak{M}$ } \tag{8}$$

$$\text{FST} \propto \Delta \text{t}\_{\text{Tmax}} - 2 : \text{30} \tag{9}$$

Therefore, the SAC method is well applicable to simple Portland cement-water mixtures in the range of 0.25–0.31 w/c. Using too much mixing water (w/c > 0.44) will cause cement paste bleeding (water separation from the cement). Excess water does not participate in the chemical reaction of setting, but at the same time, it impedes the setting process and, due to its high heat capacity, draws heat out of the system.

The applicability of the SAC method to the investigation of the setting properties of CEM I 42.5 N Portland cement was confirmed at 0.25, 0.28, and 0.31 w/c ratios. Other cement pastes or mortars and concretes prepared without admixtures and supplementary materials may behave similarly, but it needs to be verified by further testing.

#### **Acknowledgements**

The authors of this article would like to thank Dr. László Csetényi for his helpful comments and supports, as well as Dr. Tamás Kói for his help in the mathematical problems occurred.

The authors acknowledge the support by the Hungarian Research Grant NVKP\_16-1-0019 "Development of Concrete Products with Improved Resistance to Chemical Corrosion, Fire or Freeze-Thaw."

#### **List of referred standards**

EN 196–3: 2017 Methods of testing cement. Part 3: Determination of setting time and soundness.

EN 480–2:2007 Admixtures for concrete, mortar and grout. Test methods. Part 2: Determination of setting time.

ASTM C191–19 Standard Test Methods for Time of Setting of Hydraulic Cement by Vicat Needle. ASTM International. West Conshohocken. PA. 2019. DOI: 10.1520/ C0191-19

ASTM C266-20 Standard Test Method for Time of Setting of Hydraulic-Cement Paste by Gillmore Needles. ASTM International. West Conshohocken. PA. 2020. DOI: 10.1520/C0266-20

ASTM C403 / C403M-16. Standard Test Method for Time of Setting of Concrete Mixtures by Penetration Resistance. ASTM International. West Conshohocken. PA. 2016. DOI: 10.1520/C0403\_C0403M-16

ASTM C807–20. Standard Test Method for Time of Setting of Hydraulic Cement Mortar by Modified Vicat Needle. ASTM International. West Conshohocken. PA. 2020. DOI: 10.1520/C0807-20

ASTM C953-17. Standard Test Method for Time of Setting of Grouts for Preplaced-Aggregate Concrete in the Laboratory. ASTM International. West Conshohocken. PA. 2017. DOI: 10.1520/C0953-17

ASTM C1679-17. Standard Practice for Measuring Hydration Kinetics of Hydraulic Cementitious Mixtures Using Isothermal Calorimetry. ASTM International. West Conshohocken. PA. 2017. DOI: 10.1520/C1679-17

ASTM C1753 / C1753M-15e1. Standard Practice for Evaluating Early Hydration of Hydraulic Cementitious Mixtures Using Thermal Measurements. ASTM International. West Conshohocken. PA. 2015. DOI: 10.1520/C1753\_C1753M-15E01

AASHTO T131–20 Standard Method of Test for Time of Setting of Hydraulic Cement by Vicat Needle. American Association of State and Highway Transportation Officials. 2020.

AASHTO T154–18 Standard Method of Test for Time of Setting of Hydraulic Cement Paste by Gillmore. Needles. American Association of State and Highway Transportation Officials. 2018.

ISO 9597:2008 Cement-test Methods – Determination of Setting Time and Soundness. International Organization for Standardization

### **Author details**

Katalin Kopecskó\* and Attila Baranyi Faculty of Civil Engineering, Budapest University of Technology and Economics, Budapest, Hungary

\*Address all correspondence to: kopecsko.katalin@emk.bme.hu

© 2022 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

*Comparative Study of Setting Time and Heat of Hydration Development of Portland Cement… DOI: http://dx.doi.org/10.5772/intechopen.101912*

#### **References**

[1] Lootens D, Roussel N. Rheology of penetrations tests II: Penetrometers, Vicat and Hilti needles. In: Proceedings of the 12th International Congress on the Chemistry of Cement. Montreal, Canada: National Research Council of Canada; 8-13 July 2007. pp. 1-12

[2] Reinhardt HW, Grosse CU, Herb AT. Ultrasonic monitoring of setting and hardening of cement mortar—A new device. Materials and Structures. 2000; **33**:580-583. DOI: 10.1007/BF02480539

[3] Lee HK, Lee KM, Kim YH, Yim H, Bae DB. Mint: Ultrasonic in-situ monitoring of setting process of highperformance concrete. Cement and Concrete Research. 2004;**34**:631-640. DOI: 10.1016/j.cemconres.2003.10.012

[4] Sant G, Dehadrai M, Bentz D, Lura P, Ferraris CF, Bullard JW, et al. Mint: Detecting the fluid-to-solid transition in cement pastes: Comparison of experimental and numerical techniques. Concrete International. 2009;**236**:53-58

[5] Gabrijel I, Mikulić D, Milovanović B. Mint: Application of ultrasonic measurements for determination of setting and hardening in cement paste. Journal of Civil Engineering and Architecture. 2011;**5**(3):278-283. DOI: 10.17265/1934-7359/2011.03.010

[6] Taylor P, Wang K, Wang X, Wang X. Mint: Comparison of setting time measured using ultrasonic wave propagation with saw-cutting times on pavements. InTrans Project Reports. 2015;**142**:1-30. DOI: 10.13140/ RG.2.1.3907.4329

[7] McCarter WJ, Chrisp TM, Starrs G, Blewett J. Mint: Characterization and monitoring of cement-based systems using intrinsic electrical property

measurements. Cement and Concrete Research. 2003;**33**:197-206. DOI: 10.1016/S0008-8846(02)00824-4

[8] Wei X, Li Z. Study on hydration of Portland cement with fly ash using electrical measurement. Mint: Materials and Structures. 2005;**38**:411-417. DOI: 10.1007/BF02479309

[9] Li Z, Xiao L, Wei X. Mint: Determination of concrete setting time using electrical resistivity measurement. Journal of Materials in Civil Engineering. 2007;**19**:423-427. DOI: 10.1061/(ASCE) 0899-1561(2007)19:5(423)

[10] Wang K, Ge Z, Grove J, Ruiz JM, Rasmussen R, Ferragut T. Mint: Developing a simple and rapid test for monitoring the heat evolution of concrete mixtures for both laboratory and field applications. InTrans Project Reports. 2007;**153**. DOI: lib.dr.iastate. edu/intrans\_reports/153

[11] Cost VT, Gardiner A. Practical Concrete Mixture Evaluation via Semiadiabatic Calorimetry. In: Proceedings of the Concrete Technology Forum 2009, National Ready Mixed Concrete Association. Cincinnati, Ohio, USA: 13-15 May 2009

[12] Ge Z, Wang K, Sandberg PJ, Ruiz JM. Mint: Characterization and performance prediction of cement-based materials using a simple isothermal calorimeter. Journal of Advanced Concrete Technology. 2009;**7**(3):355-366. DOI: 10.3151/jact.7.355

[13] Bentz DP. Mint: Critical observations for the evaluation of cement hydration models. International Journal of Advances in Engineering Sciences and Applied Mathematics. 2010;**2**:75-82. DOI: 10.1007/s12572-010-0017-4

[14] Rolo L. Monitoring of the Cement Hydration Behavior and Determination of Non-standard Laboratory Indicators of Setting Time [Thesis]. Canales y Puertos: Ingeniería de Caminos; 2013. DOI: 10.13140/2.1.1963.6480

[15] Hu J, Ge Z, Wang K. Mint: Influence of cement fineness and water-to-cement ratio on mortar early-age heat of hydration and set times. Construction and Building Materials. 2014;**50**:657-663. DOI: 10.1016/j.conbuildmat.2013.10.011

[16] Chung C, Kim JH, Lee S. Mint: The use of semi-adiabatic calorimetry for hydration studies of cement paste. Journal of the Korea Institute of Building Construction. 2016;**16**(2):185-192. DOI: 10.5345/JKIBC.2016.16.2.185

[17] Sanderson RA, Cann GM, Provis JL. Comparison of calorimetric methods for the assessment of slag cement hydration. Advances in Applied Ceramics. 2017;**116**: 186-192. DOI: 10.1080/ 17436753.2017.1288371

[18] Kang X, Lei H, Xia Z. Mint: A comparative study of modified fall cone method and semi-adiabatic calorimetry for measurement of setting time of cement based materials. Construction and Building Materials. 2020;**248**. DOI: 10.1016/j.conbuildmat.2020.118634

[19] Egan PJ. Mint: A comparison between semi-isothermal and semiadiabatic calorimetry of retarded cement mixes. Advances in Cement Research. 1988;**1**(2):112-118. DOI: 10.1680/ adcr.1988.1.2.112

[20] Csetényi LJ. Stability of Borate-Containing Wastes Encapsulated in Cement [PhD Thesis]. United Kingdom: University of Aberdeen; 1993

[21] Han MC, Han CG. Mint: Use of maturity methods to estimate the setting time of concrete containing super retarding agents. Cement & Concrete Composites. 2010;**32**:164-172. DOI: 10.1016/j.cemconcomp.2009.11.008

[22] Bentz DP, Peltz MA, Winpigler J. Mint: Early-age properties of cementbased materials. II: Influence of waterto-cement ratio. Journal of Materials in Civil Engineering. 2009;**21**:512-517. DOI: 10.1061/(ASCE)0899-1561(2009)21:9 (512)

#### **Chapter 5**

## Calorimetry to Understand Structural Relaxation in Chalcogenide Glasses

*Balbir Singh Patial*

#### **Abstract**

Thermal behavior of chalcogen additive materials synthesized via melt quench method can be studied by reheating the bulk samples in differential scanning calorimetry (DSC) or differential thermal analyzer (DTA) experiment. It involves kinetics of structural transformations as three basic characteristic phenomena correspond to glass transition, crystallization and melting are involved. Thermal stability and glass forming ability are important factors from technological point of view in various applications. Thermal stability of glasses can be ascertained based on calorimetric measurements. In the glass transition region (first region in reheating experiment), structural relaxation takes place. The temperature in glass transition region, its heating rate dependence and empirical approaches for estimation of apparent activation energy are useful to determine utility of these materials in various applications.

**Keywords:** chalcogenide glasses, DSC or DTA, non-isothermal, structural relaxation, glass transition, activation energy

#### **1. Introduction**

Long back ago, it was believed that amorphous solids could not be semiconductors as known from the fact that that the existence of semiconductors is connected with the quantum theory of the solids, which in turn is based on the presence of long range order. The interest in amorphous materials grew in 1950's when it was found that the non-crystalline solids and liquids that do not have any periodic structure also behave as semiconductors. Since then, extensive research initiated to explore these materials. These materials have great potential to serve as raw materials for the fabrication of electronic devices and the time is not far off when crystalline materials may be completely replaced by amorphous materials in electronic industries. It is because of the fact that the preparation technique is comparatively cheaper, processes involved are comparatively easier and the devices are of good quality in amorphous field. Amorphous materials can be regarded as amorphous semiconductors, if the energy band gap lies between 0.1 eV and 3 eV. Amorphous materials are becoming progressively popular due to their wide range of applications in solid state devices.

Glasses are those amorphous solids which are prepared by rapid cooling of the melt. In principle, any substance can be made into a glass by cooling it from the liquid state fast enough to prevent crystallization. In general, glass scientists regard the term 'glass' as covering 'all non-crystalline solids that show a glass transition' irrespective of their preparation methods. In actual practice, glass formation has been achieved with a relatively limited number of substances. The two standard methods of preparing amorphous solids are: (*i*) by condensation from the vapor as in thermal evaporation, sputtering, glow-discharge decomposition of gas or other methods of deposition and (*ii*) by cooling from a melt. The first method produces thin films, while the second method provides bulk materials. Materials that are obtained by cooling from the melt are called glasses and generally have a lesser tendency to crystallize as compared with those that can be prepared only by deposition [1]. The crystallization of an amorphous material proceeds by the processes of nucleation and growth. Glass formation is inhibition of crystallization. Glass formation becomes more probable at higher cooling rate, the smaller the sample volume and slower the crystallization rate. Whether a particular liquid can be cooled to form a glass or not, will clearly depend on the rates of the atomic or molecular transport processes involved in the nucleation and crystal growth. Liquids with small crystallization kinetic constants can thus form glasses directly from the melt. This is the basic reason as to why selenium (Se) is a good glass former in contrast to pure tellurium (Te). Silicon and germanium cannot be quenched into the glassy state even at very fast quench rates. When it was proposed that chalcogenide glasses containing large proportions of one or more chalcogen elements namely sulfur (S), selenium (Se) and tellurium (Te) instead of the conventional sixth group element oxygen (O) can act as semiconductors and continuous research in this field is going on. Moreover, the possibility of doped chalcogenide glasses in the well controlled manner has opened up many new directions for the application of chalcogenide glasses in different fields.

The alloys of chalcogenide glasses have a certain range of atomic percentages of each constituent in which they can be glassy and beyond this range they are semi-crystalline or crystalline. From literature, it can be inferred that small samples say binary, ternary or multicomponent compositions were prepared, their nature (crystalline or amorphous) were determined and consequently glass formation region is mapped out for each composition. The range of glass forming region is to some extent reliant on the quench rate or the quantity of material used during the sample preparation. Chalcogenide glasses are prepared by quenching of the liquid below melting temperature. Upon cooling a liquid below its freezing temperature, it will either crystallize or to form a glass. Glasses of different compositions have different regions of glass formation directed by the type of bonds between the constituent elements. An increased tendency to glass formation is possessed by chalcogenide compounds and alloys with predominantly covalent chemical bonds. However, the specific composition upto which glass formation in binary, ternary or multi-component system is possible, cannot be predicted in priori and has to be determined experimentally. For example, in Se-Te system, glass formation is possible upto tellurium content 30 at % [2].

When glass forming liquid is cooled, some of its properties change sharply in a narrow temperature range [3, 4]. Figure shows volume versus temperature plot during the course of temperature lowering experiment (melt quenching). Continued cooling decreases the liquid volume in a continuous fashion and the slope of the smooth volume-temperature curve defining the liquid's volume coefficient of thermal expansion. Eventually, when the temperature is brought low enough, a liquid–solid transition takes place. Its signature in terms of low value of the expansion coefficient i.e. a smaller slope, characterizes a solid. A liquid may solidify in two ways; first one corresponds to route 1 (**Figure 1**) discontinuously to a crystalline solid and

*Calorimetry to Understand Structural Relaxation in Chalcogenide Glasses DOI: http://dx.doi.org/10.5772/intechopen.104418*

**Figure 1.** *Volume versus temperature plot for cooling an assembly of atoms can condense into the solid state.*

secondly via route 2 continuously to an amorphous solid (glass) (where *T*f is freezing temperature and *T*b is boiling temperature in **Figure 1**). The liquid-crystal transition occurred at freezing or melting temperature and an abrupt contraction is observed to the volume of the crystalline solid. However, at sufficiently high cooling rates in a melt-quenching experiment, the most materials are found to alter their behavior and follow route 2 to the solid phase. An abrupt change in the slope of the curve equal to the coefficient of volume expansion occurs at a certain temperature. This temperature is called the glass transition temperature (*T*g). The liquid-glass transition occurs in a narrow temperature interval near *T*g.

There is no volume discontinuity, instead curve bends over to acquire the small slope characteristic of the low thermal expansion of a solid. It is significant that viscosity does not show an abrupt change at the glass transition temperature.

#### **2. Experimental methods**

#### **2.1 Melt-quench technique**

Melt-quenching technique is a widely used method to prepare the various samples of the chalcogenide glasses. The entire equipment used for preparing the alloys consists of a furnace to prepare the melt of solid mixture, a rocking arrangement to make the melt homogenous and a quenching arrangement to rapidly cooling of the melt. The furnace is operated maximum at 120 V ac and can raise the temperature up to 1200°C or more depending on type of furnace. Quartz ampoules (outer diameter ~ 1.2 cm and inner diameter ~ 1.0 cm, length ~ 10 cm) are prepared by sealing the quartz tube on one side and a neck on other side to pour the solid mixture before evacuation. To prepare glassy alloy of type SeαInβPbγTeδ, the elemental substances (5 N) are weighed according to the exact proportions of high purity (99.999%) elements in accordance with their atomic percentages (α,β,γ,δ are the respective atomic weight percentages of Se, Te, Pb and In).

#### *Applications of Calorimetry*

The quartz ampoules are properly cleaned with soap solution, acetone, methanol and then dried by heating in the furnace at 500°C for half an hour. The weighed mixture is poured into the ampoules and these ampoules are sealed in a vacuum of ~2 × 10−5 mbar using the diffusion pump. Then ampoules are fastened to a ceramic rod and the rod is attached to the rocking arrangement. The sealed ampoules are heated in increasing order of melting points of the constituent's elements of the glassy alloys for 2 hours each. For example, in case of Se-Te-In, the temperature of the furnace is raised to 200°C for 2 hours, so that the indium [melting temperature, *T*m = 156.6°C] diffuse into the rest of the constituents. The temperature is then raised to 300°C so that the selenium (Se) [*T*m = 217°C] thoroughly mixes with other constituents. The sealed ampoules heated upto temperature 600°C in the rocking furnace initially, so that tellurium [*T*m = 449°C] in respective composition mixed properly. Later, the temperature of the furnace has been raised upto 900°C and maintained at this temperature for 24 hours and rocking is done to ensure proper mixing and homogeneity of the samples. The heated ampoules are then quickly quenched in ice cooled water to get glassy alloys.

Then tubes are broken, crushed, separated, ground to fine powder, labeled and kept in vacuum desiccators for further analysis.

#### **2.2 Differential scanning calorimetry**

The thermal behavior of the glasses is investigated using DSC system. The complete DSC system consists of the DSC analysis module, temperature controller, data analyzer and recorder/plotter for the preparation of hardcopy record. Working principle of DSC is shown in **Figure 2**. The temperature range covered in this DSC unit was from room temperature to high enough temperature (>500 degree Celsius) as per instrument make. Approximately, 3–5 mg of sample in powder form is encapsulated in standard aluminum pan in an atmosphere of dry nitrogen at a flow of 40 mL min−1 and heated as per requirement under either isothermal or non-isothermal conditions. The values of glass transition temperature (*T*g), the temperature of crystallization (*T*c), and the melting temperature (*T*m) are determined by using the microprocessor of the thermal analyzer.

#### **3. Structural relaxation in chalcogenide glasses**

Kauzmann [3] showed that glass transition occurs for many types of glasses. It has been suggested that some amorphous solids do not show a glass transition temperature (*T*g), but this result has not been established. Since 2005, when I started research in the field of chalcogenide glasses for Ph.D. degree and synthesized binary, ternary and quaternary chalcogen based glasses and even after while continuing research almost 50 samples are prepared by melt quenching technique. But these samples always found to associate with *T*g [5–9]. It is because of the fact that rearrangements in the glass structure occur during temperature lowering experiment (cooling) when the glass has the properties of liquid. Therefore, the changes are slow when the glass structure is frozen (cooling is fast enough) and it behaves like a solid. When a glass is cooled rapidly from a temperature, above the transition region into this region, it retains some properties of higher temperature. These properties 'relax' to the characteristics of the lower temperature with time may be pronounced more commonly as '*structural relaxation*'. The time to reach a stable or equilibrium state is longer at lower holding temperatures. If a glass material is cooled rapidly from a room temperature above the transition region, non-uniformities in its temperature during cooling lead to stresses in the glass. These stresses can weaken the glassy material and change its properties. So, it is desirable to remove them by heating the glass at an appropriate temperature in the transition region. At this annealing temperature, the stresses are removed as the glass relaxes. The rate at which annealing goes on is important in preparing glasses for use. The relaxation of glass structure from one set of properties to another after a rapid change in temperature in the glass transition region is called *structural relaxation*. When a glass is subjected to a stress (strain) in this region, the deformation changes with time and this process is called stress or strain relaxation. The rates of this relaxation are of practical importance and have been studied intensively in the last few years.

**Figure 3** shows a typical DSC mostly observed in reheating calorimetric experiment displaying glass transition (first endothermic peak), crystallization (exothermic peak) and melting (second endothermic peak) for a chalcogenide glass. But it is pertinent to mention here that heat flow in calorimetric measurements may

#### **Figure 3.**

*A typical DSC curve showing glass transition, crystallization and melting of a chalcogenide glass.*

be different for other materials like polymers depends on materials' characteristics. The inset of **Figure 2** shows the crystallization fraction at a generic temperature *T* (shaded area of exothermic peak). DSC curves are characterized by first occurrence of endothermic peak which corresponds to glass transition. In this process, molar volume and enthalpy of chalcogenide material change resulting in variation of specific heat and viscosity which marks transition from solid phase to super cooled liquid phase. In other words, instantaneous change in temperature during quenching causes chalcogenide glassy material to relax from a higher enthalpy to an equilibrium state of lower enthalpy and this process is called thermal relaxation. Glass transition temperature (*T*g) corresponds to point of intersection of tangents drawn to baseline and endothermic baseline shift. The onset values of characteristic temperatures are taken while defining the properties and henceforth use of glasses in technological applications. But, for in observations and hence particularly in calculations peak values of *T*g, *T*p and *T*m are taken instead of onset values because of more accuracy in measurement of peak values than onset values. Least-squares fitting method is applied to deduce apparent activation energy and other kinetic parameters while using empirical approaches. Chalcogenide glasses generally show single *T*g and single *T*p indicate that the investigated system exists in single phase and homogeneous, however, a second glass transition temperature (*T*g2) is also observed for Se-Te-Sn investigated samples see reference [6]. The existence of a second glass transition temperature directs unusual phase separation happening in thermal treatment. This phase separation, leading to presence of a second or more than two glass transition temperatures, may be thought of arising after super cooled melt transition or the glass may be in two phases or higher to start with itself. The phenomenon of presence of a second *T*g has been found in other chalcogenides [10, 11] also.

It is observed that characteristic temperatures shift to higher temperature with increasing heating rate. At *T*g, structural relaxation time becomes equal to the relaxation time of observation τob [12]. Since *T*g∝ 1/ τob. Thus, with the increase in heating rate, *τ*ob decreases leads to increased *T*g also observed in other glasses [5–9]. It can also be ascribed from heat dissipated so much easier at higher heating rate; therefore, decomposition begins on relatively higher temperature and has high heat of fusion.

*T*c is also found to increase (similar to *T*g) with increasing heating rate. This could be because the materials do not get enough time for nucleation and crystallization with higher heating rate.

#### **4. Glass transition calorimetry**

In reheating experiment of glass in calorimetry, two ways can be adopted namely isothermal and non-isothermal methods. In first method i.e. under isothermal conditions, the material under investigation is placed rapidly to a temperature above *T*g and the heat evolved at a constant temperature is noted as a function of time during the crystallization process. In the other method, i.e. under nonisothermal conditions, the material is heated at a fixed heating rate usually from room temperature. Again in this method also, heat evolved is noted as a function of time or temperature. A drawback of experiment under isothermal conditions is the impossibility of attainment a test temperature instantly and during the time, which system desires to stabilize, no observations are possible. However, the second method i.e. under non-isothermal conditions does not have this limitation. Due to above mentioned reasons; we have also applied this technique for the overall crystallization kinetics of investigated glassy alloys [5–9].

Characteristic temperature above which glassy material can have several structural arrangements and below which material is frozen in a structure which cannot change into other configuration easily is defined as glass transition temperature *T*g. *T*g is an indispensable parameter in studying stability of glassy materials. Furthermore, cohesive forces must be overcome for movement of atoms in glass network. So, *T*<sup>g</sup> must be related to the magnitude of these forces. Therefore, theoretical models are also proposed to determine *T*g which assume it to be proportional to cohesive forces, (in terms of mean bond energy *< E >)* and network rigidity*.* Tichy and Ticha [13] proposed that *T*g depend on two factors; coordination number *< r >* and *< E >* after analyzing for186 glasses; *T*g = 311[< *E* > - 0.9] (*T*g so derived is in kelvin). Lankhorst [14] also devised a model for estimation of *T*g from heat of atomization *H*s of system and suggested empirical relation; *T*g = 3.44 *H*s- 480. Tanaka also gave the exponential relationship as [15]; *T*g = *exp*(1.6 < *r* > + 2.3). Experimental values are sometimes closely matched with theoretically values.

Glass transition temperature depends upon the co-ordination number, bond energy and types of structural units formed. The glass transition region may be studied from glass transition temperature and its heat rate dependence, consequently, apparent activation energy of glass transition. Glass transition temperature represents the strength or rigidity of the glass structure of the glassy material. We employed three approaches to analyze the dependence of the *T*g on the heating rate and estimation of apparent glass transition activation energy of bulk glasses [5–9]. The first one corresponds to the empirical relation given by Lasocka [16] as *T*g = *A* + *B* ln(*α*), where *A* and *B* are constants depending upon the glass composition. From this relation, it can be easily inferred that a plot between ln(*α*) and *T*g should be a straight line. Also, *A* could be deduced as *T*g at a heating rate of 1 Kmin−1. It is suggested by other researchers that *B* (determined from slope) may be correlated to the cooling rate of the melt [17, 18]. Lesser is the cooling rate of the melt, lesser is *B*. Thus, the physical significance of *B* looks to be connected with the response of the fluctuations in the configuration within the glass transformation region.

Reheating of a chalcogenide glass result into crystallization phenomenon and studies of crystallization kinetics are always connected with the concept of activation energy. Another parameter which is comprehensively used to get into structural relaxation kinetics is apparent activation energy. It is said to be that energy which is absorbed by a assembly of atoms in this region, such that a jump from one metastable state to another is possible. This apparent activation energy is involved in the molecular motion and rearrangement of atoms around glass transition temperature. The more general method used in this regard is Kissinger's equation which is basically meant for the determination of activation energy for crystallization process. The justification of applying this method for the evaluation of the glass transition activation energy comes from the shifting of glass transition peaks at different heating rates similar to crystallization peaks. The details of this method can be noted from [19, 20] and in case of glass transition it is modified to (α/*T*<sup>g</sup> 2 ) = − *E*g/ *RTg* + *constant*. Slope of the plot between ln(α/*T*<sup>g</sup> 2 ) and 1/*T*g is utilized to derive *E*g. We have also used this method extensively to deduce *E*g, establish a relation with other experimentally deduced parameters and thereafter to draw conclu-

sions regarding thermal stability among the investigated glasses [5–9]. The other approach, using heating rate dependence of *T*g is also used defined by Moynihan *et al* [21] in terms of the thermal relaxation phenomenon. In this kinetic interpretation, the enthalpy at a particular temperature and time *H* (*T*, *t*) of the glassy system, after an instantaneous isobaric change in temperature, relaxes isothermally toward a new equilibrium value *H*e(*T*). The relaxation equation can be written in the following form [22]:

$$\left(\frac{\delta H}{\delta t}\right)\_T = -\frac{\left(H - H\_\circ\right)}{\pi} \tag{1}$$

where τ is a temperature—dependent structural relaxation time and is given by the following relation:

$$x = r\_o \exp\left(-E\_\kappa \, ^\circ RT\right) \exp\left[-c\left(H - H\_\circ\right)\right] \tag{2}$$

where *τ*o and *c* are constants and *E*g is the activation energy of relaxation time. Using the above equations, it can be shown [21–23] that ln(*α*) = − *E*g/*RT*g + *constant*. Similarly, in this method i.e. using Moynihan's relation, slope of the linear fit variation of ln(α) against 1/*T*g gives *E*g. *E*g values so deduced are found in concordance with Kisinger's relation [5–9]; therefore, one can use either of these two approaches.

Thermal stability and the ease of glass formation is a major issue in the study of glassy materials as it determines the degree of utilizing the investigated materials in various applications. It can be ascertained based on calorimetric observations. Kauzmann proposed two-third rule to determine the ease in glass formation [3] as *T*rg = *T*g/*T*m. The composition obeying two-third rule (*T*rg ≥ 0.65), indicating that the glass forming ability (*GFA*) for that composition of the material is high.

For a memory and switching material, the thermal stability and *GFA* are of vital importance. Glass transition temperature also gives the worthwhile information about the thermal stability related with strength and rigidity of glass structure. GFA is also associated with cooling of the melt bypassing crystallization. It has been stated that (*T*c-*T*g) is also an indicator of GFA. Higher the value of this difference, greater is GFA because higher values of this difference indicate the more kinetic resistance to crystallization. One more parameter, Hruby number *K*gl is important by which thermal

#### *Calorimetry to Understand Structural Relaxation in Chalcogenide Glasses DOI: http://dx.doi.org/10.5772/intechopen.104418*

stability and glass formation is evaluated as (*T*c-*T*g)/(*T*m-*T*c) [24]. Higher (*T*c-*T*g) delays nucleation while lower (*T*m-*T*c) retards growth in nucleated crystals. Thus, Hruby's parameter merges nucleation and growth information during amorphouscrystallization phase transformation. Thus, Hruby's parameter combines the nucleation and growth aspects of phase transformation. Therefore, the composition of the glass with higher value could be taken as the most stable among studied samples.

There is no absolute measurements to define the glass formation, the empirical methods extensively used for its quantifiable properties. The fragility index (*F*i) is a significant parameter to define glass forming ability and it is a measure of the rate at which the relaxation time decreases with the increase in temperature around glass transition temperature. This distict parameter is given by the relation [25, 26]; *Fi = Eg/RTgln*(*α*). According to Vilgis [27], the glass forming liquids that show an approximate Arrhenian temperature dependence are defined as strong and specified with a lower value of *F*i (*F*i *≈* 16), while the other side limit i.e. fragile glass forming liquids categorized by a higher value of *F*i *(F*i *≈* 200). Thus, it is reasonable to state that the glasses having values of *F*i within the above mentioned limit has been obtained from the good glass forming liquids.

#### **5. Conclusions**

In this chapter, use of calorimetry is discussed to understand structural relaxation in chalcogenide glasses. Some of theoretical approaches are also mentioned here that are generally used to estimate glass transition temperature before calorimetric experiment. Further, the usage of experimental data obtained from DSC or DTA for derivation of different parameters and apparent activation energy of glass transition region and hence understanding relaxation kinetics in glass transition region is also discussed in detail.

#### **Author details**

Balbir Singh Patial Department of Physics, Himachal Pradesh University, Shimla, Himachal Pradesh, India

\*Address all correspondence to: bspatial@gmail.com; bspatial@hpuniv.ac.in

© 2022 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

### **References**

[1] Mott NF, Davis EA. Electronic Processes in Non-crystalline Materials. Oxford: Clarendon Press; 1979. p. 200

[2] Odelevskii VI. The calculation of the generalized conductivity of heterogeneous systems. Journal of Technical Physics (USSR). 1951;**21**:678-685

[3] Kauzmann W. The nature of the glassy state and the behavior of liquids at low temperatures. Chemical Reviews. 1948;**43**:219-256. DOI: 10.1021/ cr60135a002

[4] Zallen R. The Physics of Amorphous Solids. Weinheim: WILEYNCH Verlag GmbH & Co. KGaA; 1983

[5] Patial BS, Thakur N, Tripathi SK. On the crystallization kinetics of In additive Se–Te chalcogenide glasses. Thermochimica Acta. 2011;**513**:1-8. DOI: 10.1016/j.tca.2010.09.009

[6] Patial BS, Thakur N, Tripathi SK. Crystallization study of Sn additive Se–Te chalcogenide alloys. Journal of Thermal Analysis and Calorimetry. 2011;**106**(3):845-852. DOI: 10.1007/ s10973-011-1579-5

[7] Anjali Patial BS, Bhardwaj S, Awasthi M, Thakur N. On the crystallization kinetics of multicomponent nano-chalcogenide Se79-*x*Te15In6Pbx (*x* = 0, 1, 2, 4, 6, 8 and 10) alloys. Nano Express. 2020;**1**(3):030021. DOI: 10.1088/2632-959X/abc8c7

[8] Sharma N, Bhardwaj S, Thakur N, Patial BS. Crystallization study of Pb additive Se-Te-Ge nanostructured alloys using non-isothermal differential scanning calorimetry. Nanofabriaction. 2022

[9] Patial BS, Thakur N, Tripathi SK. A non-isothermal crystallization study of chalcogenide Se85Te15 glass using

differential scanning calorimetry. Physica Scripta. 2012;**85**:045603. DOI: 10.1088/0031-8949/85/04/045603

[10] Abdel-Rahim MA, Hafiz MM, Shamekh AM. A study of crystallization kinetics of some Ge–Se–In glasses. Physica B: Condensed Matter. 2005;**369**(1-4):143-154. DOI: 10.1016/j. physb.2005.08.007

[11] Lafi OA, Imran MMA, Abdullah MK. Glass transition activation energy, glass-forming ability and thermal stability of Se90In10−*x*Snx (*x*=2, 4, 6 and 8) chalcogenide glasses. Physica B: Condensed Matter. 2007;**395**:69-75. DOI: 10.1016/j.physb.2007.02.026

[12] Zheng Q, Zhang Y, Montazerian M, Gulbiten O, Mauro JC, Zanotto ED, et al. Understanding glass through differential scanning calorimetry. Chemical Reviews. 2019;**119**(13):7848-7839. DOI: 10.1021/ acs.chemrev.8b00510

[13] Tichy L, Ticha H. Covalent bond approach to the glass-transition temperature of chalcogenide glasses. Journal of Non-Crystalline Solids. 1995;**189**:141-146

[14] Lankhorst MHR. Modelling glass transition temperatures of chalcogenide glasses. Applied to phase-change optical recording materials. Journal of Non-Crystalline Solids. 2002;**297**:210-219. DOI: 10.1016/S0022-3093(01)01034-1

[15] Tanaka K. Glass transition of covalent glasses. Solid State Communications. 1985;**54**:867-869. DOI: 10.1016/0038-1098(85)91158-5

[16] Lasocka M. The effect of scanning rate on glass transition temperature of splat-cooled Te85Ge15. Materials Science *Calorimetry to Understand Structural Relaxation in Chalcogenide Glasses DOI: http://dx.doi.org/10.5772/intechopen.104418*

and Engineering. 1976;**23**:173-177. DOI: 10.1016/0025-5416(76)90189-0

[17] Calventus Y, Suriñach S, Baró MD. Thermal stability and crystallization kinetics study of some Se-Te-Ge glassy alloys. Materials Science and Engineering A. 1997;**226-228**:818-822. DOI: 10.1016/S0921-5093(96)10801-7

[18] Mehta N, Singh KS. Effect of Sb and Sn additives on the activation energies of glass transition and crystallization in binary Se85Te15 alloy. Phase. Transit. 2009;**82**:43-51. DOI: 10.1080/01411590802260084

[19] Kissinger HE. Variation of peak temperature with heating rate in differential thermal analysis. Journal of Research of the National Bureau of Standards. 1956;**57**:217. DOI: 10.6028/ jres.057.026

[20] Kissinger HE. Reaction kinetics in differential thermal analysis. Analytical Chemistry. 1957;**29**:1702-1706. DOI: 10.1021/ac60131a045

[21] Moynihan CT, Easteal AJ, Wilder J, Tucker J. Dependence of the glass transition temperature on heating and cooling rate. The Journal of Physical Chemistry. 1974;**78**:2673-2677. DOI: 10.1021/j100619a008

[22] Larmagnac JP, Grenet J, Michon P. Glass transition temperature dependence on heating rate and on ageing for amorphous selenium films. Journal of Non-Crystalline Solids. 1981;**45**(2):157- 168. DOI: 10.1016/0022-3093(81)90184-8

[23] Kasap SO, Juhasz C. Kinematical transformations in amorphous selenium alloys used in xerography. Journal of Materials Science. 1986;**21**:1329-1340. DOI: 10.1007/BF00553271

[24] Hrubý A. Evaluation of glass-forming tendency by means of DTA. Czechoslovak Journal of Physics. 1972;**22**:1187-1193. DOI: 10.1007/BF01690134

[25] Saffarini G, Saiter A, Garda MR, Saiter JM. Mean-coordination number dependence of the fragility in Ge-Se-In glass-forming liquids. Physica B: Condensed Matter. 2007;**389**:275-280. DOI: 10.1016/j.physb.2006.06.163

[26] Štrbac GR, Petrović JS, Štrbac DD, Čajko K, Lukić-Petrović SR. Glass transition kinetics and fragility index of chalcogenides from Ag-As-S-Se system. Journal of Thermal Analysis and Calorimetry. 2018;**134**:297-306. DOI: 10.1007/s10973-018-7151-9

[27] Vilgis TA. Strong and fragile glasses: A powerful classification and its consequences. Physical Review B. 1993;**47**:2882-2885. DOI: 10.1103/PhysRevB.47.2882

#### **Chapter 6**

## Cone Calorimetry in Fire-Resistant Materials

*Rakesh Kumar Soni, Meenu Teotia and Aakansha Sharma*

#### **Abstract**

Polymeric materials are specifically designed by compounding with additives to achieve specific properties that make them suitable for a particular application. Flame retardant materials offer fire-resistant properties to the polymers. The fire behavior of polymeric materials can be investigated with the help of various analytical techniques such as Underwriters Laboratories test standard UL-94, LOI test, Thermal gravimetric analysis (TGA) and Cone Calorimetry. Among these tests, Cone Calorimetry is the most suitable test method for predicting the real-scale fire behavior of polymeric materials and is adopted by the International Organization for standardization (ISO 5660-1). It quantifies heat generation, smoke production, mass loss and helps in the selection of polymeric materials for desired applications. In this chapter, an attempt has been made to present an overview of the thermal decomposition of polymers and the action of flame retardants. Different fire testing techniques generally used for investigations of fire characteristics of polymers are summarized.

**Keywords:** cone calorimetry, fire retardants, polymers, TGA, LOI

#### **1. Introduction**

Fire is a unique destructive force that thermally oxidizes polymeric materials. Fireresistant materials can withstand high temperatures and resist burning. These may be inherently flame retardant or can be made fire resistant by adding flame retardants. Flame retardants are chemical substances that are incorporated in polymeric systems to combat fire risks hence the use of flame retardants in polymeric systems play a crucial role. Employment of flame retardants never signifies the absence of fire but flame retardants retard the ignition, growth and propagation of fire, thus minimizing fireinduced destruction [1, 2]. An increase in demands for polymers due to their wide applications in thermal, electrical and mechanical sectors has rekindled the flammability issues of flame retardants with polymers and created challenges for modern technology [3–5]. An exemplary flame-retardant system should have resistance to fire ignition, high combustion speed, smoke production and toxicity without economic penalty [2]. As polymers are organic compounds, they produce volatile combustible products when subjected to heat. Flame retardants interfere with the combustion process of polymers at various stages such as decomposition, ignition, the spread of flame and also smoke process [6]. Polymer flammability is defined by many processes and/or characteristics, including burning rates (solid degradation rate and heat release rate), spread rates

(flame, pyrolysis, burn-out, smolder), ignition characteristics (delay time, ignition temperature, critical heat flux for ignition) [7], emission distribution (particularly toxic species emissions), smoke production. Several testing techniques are employed to analyze the fire behavior of polymers such as Underwriter's laboratories test standards (UL-94), limiting oxygen index (LOI) test, thermogravimetric analysis (TGA) and Cone calorimetry. In this chapter brief overview of the thermal decomposition of polymers and fire retardants & their mechanisms is presented under headings 2&3. Different types of flammability/fire tests used to analyze the fire characteristics of polymers are discussed under heading 4. It also covers the instrumental set up of the Cone calorimeter along with fire parameters obtained with the help of the instrument. Heading 5 concludes the advantages of Cone calorimetry over other analytical techniques used to determine fire characteristics of polymers.

#### **2. Thermal decomposition of polymers**

The physical and chemical properties of solid polymeric material change when heat is supplied to them as a result of thermal decomposition and thermal degradation. Thermal decomposition is a process in which extensive chemical changes can occur due to the application of heat. On the other hand, thermal degradation leads to loss of physical, mechanical and electrical properties of material when heat or elevated temperature is applied. To correlate the thermal properties of the material to the fire parameters, the process of thermal decomposition of the materials plays a crucial role. Thermal decomposition via chemical reactions generates gaseous flammable volatiles. When the flame is applied to polymeric substances, it tends to release flammable volatiles since polymer substances undergo pyrolysis. It releases some combustible gases, along with non-combustible gases (**Figure 1**). If the concentration of volatiles is at or above the combustible boundary then only it supports combustion otherwise flame dies out. Due to the presence of air, combustible products lead to flame and produce huge amounts of thermal energy, which in turn feed fire [8].

When thermal decomposition of deeper layers of solid polymeric material continues, the volatiles produced pass through the char layer formed to reach the surface. During this process, the char may cause secondary reactions to occur in the volatiles. Carbonaceous chars can be foamy layers, which slow down the decomposition of polymers considerably. Inorganic remains, on the other hand, can form glassy coverings that may then become impenetrable to volatiles and protect the beneath layers from any further thermal breakdown [9, 10]. Main chemical decomposition mechanisms are; (a) random-chain scission, in which chain scissions occur at random sites in the polymer backbone (b) end-chain scission, in which individual monomer units are consecutively removed at the chain end; (c) chain-stripping, in which atoms or groups not part of the polymer chain is cleaved; and cross-linking, in which bonds are created between polymer chains. Virgin polymer materials get decomposed by these processes. The reported literature indicates some type of correlation between mechanisms of polymer degradation and fire retardancy pathways. **Table 1** represents the polymer degradation mechanism of some synthetic polymers along with products evolved such as water, hydrocarbons and other volatiles.

The chemical processes involved in thermal decomposition are variably complex and the structure of polymers also influences the end consequence of decomposition. The chemical structure of repeating units and their heat-releasing capacity effects the fate of ignited polymer. Higher aliphatic molecules have a high potential for heat release which directly contributes to the thermal stability of the polymer [11].

**Figure 1.** *Thermal decomposition of polymers.*


**Table 1.** *Volatile products and flame retardant mechanism of polymers [12].*

#### **3. Fire retardants and their actions**

Fire exists as a unique destructive force and results in damage to life and property if not handled carefully. Nowadays polymers are used in every walk of life and therefore their properties whether chemical or mechanical are very important parameters for their application in a particular product. In applications where fire retardance is an important requisite, polymers used must possess fire retardant ability to combat the unwanted risk of fire. Generally, polymers are made fire resistant by incorporating compounds, which are known as Flame retardants imparting flame retardance to the polymers. These can be thermoplastics, thermosets, fabrics, coating and prevent or inhibit the spread of fire. The word "flame retardant" describes a function rather than a chemical family. Flame retardants are made up of a range of compounds with various characteristics and structures, and these chemicals are frequently combined for increased efficacy [13, 14]. The action of flame retardants can be classified in three ways:

#### **3.1 Vapor phase inhibition**

When flame retardant chemicals react with the burning polymer during the radical gas phase, vapor phase inhibition occurs. These additives reduce or suppress the supply of combustible gases by interfering with the creation of free radicals, cooling the system, and lowering or suppressing the generation of free radicals. Brominated flame retardants (BFRs) are commonly utilized because of their vapor phase blocking characteristics. Before the material achieves its ignition temperature, bromine releases active bromine atoms into the gas phase. These atoms inhibit the chemical process occurring well within the flame, extinguishing or delaying its spread. This allows families or employees more time to flee the building or suppress the fire in another way.

#### **3.2 Solid phase char formation**

During a fire, solid-phase char flame retardants encourage the development of char. These additives reacted with the burning polymer, forming a carbon containing layer on the surface of the material. This layer acts as a protective barrier, preventing the discharge of flammable gases and shielding the underneath material from the heat of such flame.

#### **3.3 Quench and cool system**

To increase flame resistance, quench and cool systems depend on hydrated materials. When hydrated minerals are exposed to fire, they emit water molecules that cool the substrate and interfere with the burning process.

#### **4. Types of flammability/fire tests**

Flammability testing is an important component of assuring safe and dependable consumer products. Textiles and consumer products, aircraft and transportation, mattresses, and furniture materials are among industries that use flammability test

procedures. Flammability testing methods determine how readily materials ignite, burn, and respond when they are ignited. These include the following fire tests [15]:

#### **4.1 UL-94 test (underwriters laboratories test standard UL-94)**

One of the most commonly used flammability tests for estimating comparative flammability for plastic materials is UL 94 (Underwriters Laboratories test standard UL 94). Under specified laboratory circumstances, it analyzes a sample capacity to extinguish a flame after ignition as well as its dripping behavior in respect to a small naked flame or radiant source of heat [15]. Depending on the specifications, the materials are arranged vertically or horizontally over a Bunsen burner. During a vertical flammability test, the length of time a material burns after the initiating flame is withdrawn, the amount of the specimen that burns and whether or not it drops flaming particles are all measured. Horizontal flammability tests, on the other hand, look to see if the material burns after the test flame has been withdrawn, and then determine the rate at which the specimen burns. This fire test is intended to provide as a preliminary indicator of a plastic's acceptability to be used as part of an equipment or appliance in terms of flammability. The UL 94 standard is used to determine the intensity and characteristics of combustion based on the standard samples. UL-94 test is broadly classified into UL-94 VB and UL-94 HB [16].

The UL94 vertical burning test is a popular fire testing method for industrial polymeric products and materials. A 1/2" 5" specimen is used for this test, which is held vertically at one end. The open end of the specimen is exposed to a burner flame at two 10-second periods, separated by the time required for the flaring combustion to stop after the first application [17]. The specimens are divided into two groups of five each. For each specimen, the following data is kept: (1) After the initial burner flame is applied, the duration of igniting combustion is calculated, (2) After the second burner flame is applied, the duration of blazing combustion is measured, (3). After the second burner flame is applied, the duration of glowing combustion is measured, (4) If burning droplets ignite cotton is put beneath the specimen and (5). If the specimen burns up while being held in the clamp.

Horizontal UL-94 Test is typically regarded as the easiest test to pass. The sample is clamped horizontally on the U-shaped frame and ignited in the combustion chamber for 15 seconds with a specified tiny flame. The flame is lit at one end of the specimen to determine the time it takes for the flame to spread to a certain extent and the distance at which it burns. A 1/2″ <sup>5</sup>″ specimen is used in the test, which is held horizontally at one end with markings at 1″ and 5″ from the open end. For 30 seconds or until the flaming front reaches the 1-inch mark, a flame is applied to an open-end "a mark if the combustion persists, the timer is set between the 1" and 5″ marks. If the combustion process comes to a halt before the 5th minute, "The damaged length between the two markers, as well as the duration of combustion, is all recorded [16].

#### **4.2 LOI (limiting oxygen index) test**

Charles P. Fennimore and Fred J. Martin proposed the Limiting Oxygen Index (LOI) for the first time in 1966 [18]. It's a term that has been used to describe the relative flammability of various materials. The LOI test is subject to an international standard that is standardized in France (NF T 51-071) and the United States (ASTM D 2863) (ISO 4589). The limiting oxygen index (LOI) is the lowest oxygen concentration that will allow a polymer to burn. It is given as a percentage. It's determined by

flowing a combination of nitrogen and oxygen over a burning material and gradually decreasing the oxygen level until the critical level is achieved. Standard tests, such as the ISO 4589 and ASTM D2863, are used to establish LOI values for various polymers. The limiting oxygen index is still the most important sorting criteria for polymer ignitability (LOI). The minimal oxygen content in the air for polymeric ignition and burning is determined by this method. As air contains 21% oxygen, polymers with LOI less than 21% are considered flammable, whereas those with LOI greater than 21% will not ignite in normal air. In reality, materials having an LOI of at least 25% should be less ignitable. Although, LOI is useful for proving polymer ignitability, it only provides limited evidence of material characteristics when exposed to heat, flames, or both [19, 20].

The test sample is vertically placed in a glass chimney, and then an oxygen/nitrogen atmosphere is created by a flow from the chimney's base. The flame is sparked at the top portion of the test sample, and thus the oxygen content in the flow is reduced until the flame can no longer be produced. The specimens are exposed to one or more specified sets of laboratory test conditions in this test technique. This is not always possible to detect changes in the fire-test-response characteristics assessed by or from this test if alternative test circumstances are substituted or the end-use conditions are modified. As an outcome, the results are only valid for the conditions indicated in the test procedure for exposure to fire [21].

#### **4.3 TGA (thermal gravimetric analysis)**

Thermo gravimetric analysis, often known as thermal gravimetric analysis (TGA), is a type of thermal analysis that measures the mass of a sample over time as the temperature varies. Physical events like as phase transitions, absorption, adsorption, and desorption, along with chemical phenomena such as chemical adsorption, thermal breakdown, and solid–gas interactions, are all revealed by this measurement (e.g., oxidation or reduction) [22]. The fundamental premise of thermo gravimetric analysis (TGA) has been that a sample's mass change may be evaluated under predetermined conditions. Absorption, adsorption, desorption, vaporization, sublimation, breakdown, oxidation, and reduction are all examples of thermal phenomena that TGA is used to explain [23]. Applications of TGA include, determination of thermal stability of materials (describes the breakdown mechanism, as well as the fingerprint materials, are used for identification and quality assurance), oxidative stability of materials, the composition of multi-component systems, estimated lifetime of a product, decomposition kinetics of materials, the effect of reactive or corrosive atmospheres on materials and moisture & volatiles content of Materials. This technique assists in investigations of fire characteristics of flame retardant polymers. Ureyen and Kayank investigated the effect of zinc borate with phosphorous-based FR finishing agents using cone calorimetry and TGA analysis [24]. TGA and DTA plots of zinc borate provided mass loss data of the samples which were further supported by heat release rate curves obtained from Cone Calorimetry. TGA measures thermal degradation and it can be related to flame resistive data of the samples.

#### **4.4 Cone Calorimetery**

The study of the thermal decomposition of polymers is important in terms of their fire performance behavior. This issue has been highlighted earlier by Van Krevelen [25], for many polymers, the limiting oxygen index [26] (primary test of

#### *Cone Calorimetry in Fire-Resistant Materials DOI: http://dx.doi.org/10.5772/intechopen.101976*

flammability) could be linearly related to char yield as measured by Thermogravimetric analysis under specified conditions. The authors computed the char yield of various polymers with the help of structural parameters and found general low flammability linearly dependent on minimum thermal decomposition. Later on, some cases were noted in which low thermal stability and low flammability were found simultaneously in the polymeric substances. This raises a big question mark on the reliability of thermal decomposition of polymers and its correlation with the LOI test for predicting fire performance of polymeric materials [27, 28]. Later on, Lyon and Walters [29] gave a pathway to the preliminary prediction of fire performance of the polymers from heat release data derived from thermoanalytical data. Heat releasing capacity and the rate of heat release can be considered as important parameters to predict the fire performance of the material. Cone calorimetric analysis is considered one of the reliable techniques to comment on fire performance [30–35].

The fire community pushed for dependable bench-scale instruments to assess material flammability depending on heat release rate in the late 1970s and early 1980s. Heat release rates were believed to be the most dependable and accurate indicator of a material's flammability. The Cone Calorimeter, developed by NIST's Fire Research Division (formerly known as the Center of Fire Research at the National Bureau of Standards), was launched in 1982 as the next-generation device for determining material flammability [36].

A cone calorimeter is a device that is used to examine the condensed phase fire behavior of tiny samples of diverse materials. In the area of fire safety engineering, it is frequently utilized [37]. It collects information on the sample's burning characteristics, such as heat release rate, ignition time, combustion products, mass loss and other factors [38]. Huggett's principle states that the gross heat of combustion of any organic substance is proportional to the quantity of oxygen required for burning. This concept is used to calculate the heat release rate [39]. The Cone is a fire-testing device that works on the concept that the amount of heat generated by a burning sample is proportional to the amount of oxygen used during combustion. The intensity of a fire, such as fire development rate, is directly proportional to the amount of heat a substance generates.

#### *4.4.1 Instrumentation setup*

As it offers a lot of information with tiny samples, the cone calorimeter is the most commonly used device for studying the fire behavior of materials. ASTM E1354 and ISO 5660 have been used to standardize the procedure. The fundamental idea is to detect the decreasing oxygen content in flammable gasses of a sample (100 100 4 mm3 ) exposed to a certain heat flux (10–100 kW/m2 ) [40]. A cone calorimeter is made up of several components and gadgets. Several parameters such as temperature, gas flow, mass and concentration are measured, logged, set, and adjusted by these parts when used together. The sample is mounted on a metal sample holder that is mounted on the load cell. During the experiment, the load cell records the sample's weight. Sample holders can be divided into two groups. The sample holder's edges may be open or closed, depending on the sample. If the sample is intumescent (that is, it swells and develops a protective char layer), a wired grid can be used to maintain it in place as it swells. When testing horizontally and with an edged framed sample holder, the wired grid is used. Below the cone heater is a spark igniter, which is placed directly above the sample surface. When the sample is heated, this ignites the flammable vapors that are escaping. The igniter is switched off and shifted to the side after the entire sample area has burned. A water-cooled heat flux measurement instrument is positioned on the sample surface level before the experiment during calibration. The temperature of the cone heater is then adjusted until the desired heat flux is achieved at the specimen's surface. The cone is usually positioned horizontally, although it can also be put vertically.

The form of the heater inspired the name of this testing device. Over 3 m long resistive heating wire packed with magnesium oxide refractory is coiled into a conical form to make the heater. The flue gases out from the flaming sample are gathered in an extraction chamber above the heater. The flow rate of combustion products is controlled by a flue gas fan installed in the flue gas line. In the flue gas line, the gas sampling ring is located before the fan. The gas sampling in the circle is first passed by two filters to remove pollutants, then via a cold trap and a drying agent to eliminate any potential water before contacting the gas analyzers. A smoke measuring system is located between both the gas sampling ring as well as the fan. A laser photometric beam detects the quantity of smoke generated [41, 42].

#### *4.4.2 Important fire parameters determined by cone calorimeter*

#### *4.4.2.1 Heat release rate and Total heat release*

Cone Calorimeter measures heat release rate at different incident heat fluxes. This measurement is based upon the principle that a nearly constant amount of heat is released per unit mass of oxygen consumed [43]. The concept of heat release rate calorimetry is simply the measurement of the rate at which a known weight (volume or area) of a carefully prepared specimen releases heat when exposed to a prescribed and controlled heating environment. Oxygen concentration in the flue gases is used to calculate the heat release rate. Oxygen consumed during combustion has been shown proportional to the heat released from a fuel [44]. Heat release rates and total heat released for a given time period are obtained from the strip chart record of changes in the fuel consumption required to maintain a constant temperature in the exhaust gases from the particular instrument. The traces record the decrease in fuel flow that is equivalent to the fuel contribution of the sample. An instantaneous heat release rate, expressed in watts/cm<sup>2</sup> area of the sample, is obtained by multiplying the net scale deflection at a given time by the calibration constant. The total heat release for a particular time interval was derived by graphic integration of the area under the curve between the desired time limits. The convention was established that zero time was the moment the sample "saw" the radiant flux in the exposure chamber (i.e., time was measured from the moment the door was closed). The average heat release rate for a given time period was obtained by determining the area under the curve (i.e., total heat released) and dividing by the time period of interest. In practice, this averaging is done for each successive 1-minute interval under the curve.

The heat release rate is an important parameter in determining the fire characteristics of materials. Holdsworth et al., in the year 2014 investigated different metal oxalates blended with Polyamide 6, 6 using cone Calorimetry at a heat flux of 50 kw/ m<sup>2</sup> for peak heat release rates and found lowest PHRR (peak heat release rate) for halogenated composites showing better flammability resistance [45]. The authors further added metal complexes in Polyamide 6, 6 and obtained data for various fire parameters such as ignition time, THR, HRR and PHRR [46]. These formulations were also investigated for LOI values which were not found in agreement with Cone calorimetric data. This disagreement in LOI values with cone calorimetric data was

#### *Cone Calorimetry in Fire-Resistant Materials DOI: http://dx.doi.org/10.5772/intechopen.101976*

indicated towards cross-linking and increment in char formation. Hence LOI values cannot be considered as sufficient data to comment upon fire characteristics of the material. Ramgobin et al., used the Cone Calorimetry technique to observe metal salen complexes as a fire retardant for thermoplastic polyurethane (TPU) [47]. Salen complexes of nickel, manganese and copper were fabricated in TPU and the comparative curves of heat release rates gave an idea of the best formulation based on PHRR and THR values. The lowest is PHRR and HR, better is the flame resistance performance of the sample. The width of the peak implies the release of combustibles at a broad range of temperature. Therefore, from THR data, it was found that formulations of TPU incorporated with metal complexes have at least 15% lower HR values than neat TPU. Recently, copper salen complexes were incorporated in PVC samples to study their flame resistive effect. It was found that from the cone calorimetric data that the complexes were improving fire retardance of PVC sheets only at 1 phr concentration. A decrease of 15.41 MJ/m<sup>2</sup> in total heat released was observed in PBr0 and of 10.42 MJ/m<sup>2</sup> in PBr1 sheets for the control sample sheet [48] as represented pictorially in **Figure 2**.

#### *4.4.2.2 Char*

The properties of the char and the underlying sample determine the time at which the stresses in the char layer are relieved by cracking and spalling, with subsequent reduction in the protective effects of the char layer. The finer and more uniform the texture of the sample, the longer the char layer is expected to remain intact. Schaffer showed that the charring rates of samples generally decrease as the density increases [49]. McLean attributed this effect to the variation of thermal diffusivity with density

**Figure 2.** *Effect of fire retardants on the heat release rate.*

[50]. Thermal diffusivity, a measure of how quickly a material absorbs heat from its surroundings, is defined as the ratio of thermal conductivity to the product of density and specific heat: a = (k/pC).

#### *4.4.2.3 Mass loss rate*

The rate of weight loss of a burning material has also been used as a measure of the rate of energy released during burning. The weight loss rate is directly related to the rate of heat release only in those cases where fuel composition and combustion efficiency remain constant as burning progresses [51].

#### *4.4.2.4 Smoke release*

Cone calorimeter also provides smoke production data which is often unused for predicting fire characteristics of polymers. Sonnier et al., in the year 2019 proposed new insights into the investigation of smoke production using a cone calorimeter [52]. The authors correlated smoke release to heat release using pure and flame retarded polymers, the carbon fractions and the presence of aromatic groups.

#### *4.4.3 Interpretation of results by cone calorimeter*

The cone calorimeter is an appropriate technique for evaluating the smoke suppression and fire retardance behavior of polymer samples. The cone calorimetric test is one of the most accurate methods for determining the fire resistance of polymeric materials. The overall heat release rate (HRR), peak heat release rate (PHRR), ignition duration, char yield, and smoke concentration of the sample are all determined by this test. The fire parameters can be determined by bench-scale test methods illustrated as arbitrary scale evaluation and FO- category models. The least correlation was found between these two test methods when applied on PVC panels and other polymeric materials.

Fire behavior analysis can be done through Petrella arbitrary scales, Östman and Tsantaridis model and Hansen & Hovde model [53, 54]. Two parameters, the flashover propensity 'x' (in kW/m2 s) and THR 'y' (in MJ/m<sup>2</sup> ) were proposed by Petrella for studying the contribution of the materials to flashover and thermal contribution [55]. The *x* and *y* values are helpful in determining the risk factor of the materials to thermal and flashover contribution under fire hazards.

$$\kappa = \frac{peak(HGR)}{t\_{\text{ig}}} \tag{1}$$

$$y = THR = \int\_0^\infty HGR(t)dt\tag{2}$$

The total heat released (gross heating value, in MJ/m<sup>2</sup> ) is calculated by Eq. (3) and average heat generation rates; T60 (over 60 s After ignition), T180 (over 180 s After ignition) and T300 ((over 300 s After ignition (kW/m<sup>2</sup> )) are calculated using Eqs. (4)–(6) respectively.

$$THR = \int\_0^\infty HGR(t)dt\tag{3}$$

*Cone Calorimetry in Fire-Resistant Materials DOI: http://dx.doi.org/10.5772/intechopen.101976*

$$\overline{T}\_{60} = \frac{1}{60} \int\_{\text{tig}}^{\text{tig}+60} HGR(t)dt \tag{4}$$

$$\overline{T}\_{180} = \frac{1}{180} \int\_{t\text{ig}}^{t\text{ig}+180} HGR(t)dt\tag{5}$$

$$\overline{T}\_{300} = \frac{1}{\mathbf{300}} \int\_{t\text{ig}}^{t\text{ig}+300} HGR(t)dt\tag{6}$$

Östman and Tsantaridis presented a relatively simple empirical linear regression model for the prediction of time to flashover in the room corner test. The model is based on empirical data, and was found to predict time to flashover with good accuracy for several products. Cone calorimeter results from tests at incident radiation heat flux of 50 kW/m<sup>2</sup> are used as input data to this model, which also requires information about the mean density of the tested product.

Cone calorimeter data can be used to derive useful information on studying the fire behavior of polymers. Based on the data and rational developed models, prediction of flashover time leading to fire behavior classification is feasible. Pyrolysis dynamics will help the understanding of the fundamental thermal behavior of materials leading to macroscopic fire behavior [56].

#### **5. Advantages of cone calorimeter**

Cone calorimetric test is one of the reliable tests to comment on the fire performance of polymeric substances. This test gives precise results about total heat release rate, peak heat release rate, ignition time, char yield, the smoke concentration of the sample. The best parameter for predicting fire hazard of a polymer is HRR (Heat Release Rate) in flaming combustion, although determination of HRR is a complex task for solid samples as it depends upon the heat flux, sample thickness, sample position, ventilation, etc. The justification for the widespread use of LOI test in its present form in flammability research is questionable. Aside from convenience and precision, it has many unfavorable features. Since it is a downward-burning test, this is a fire configuration of minor importance in real fires. Moreover, in the LOI test, characteristics of the heat transfer and rate of burning are fundamentally different from those in the much more important upward burning configuration. The LO1 has the unreal feature of being run at oxygen concentrations usually above the normal oxygen content of air, conditions which are probably important only in some space vehicles and oxygen contents in hospitals. It has poor thermal coupling between flame and substrate, and it is prone to severe disturbance by melt-flow phenomena. These are the ignition conditions well defined in the ASTM D2863 version of the oxygen index test. Probably the most severe deficiency of the LOI, is the lack of correlation with heat release results, is that it does not, except in unusual cases, predict the real fire performance of materials. It is still not clear whether any of the fire tests would provide enough energy feedback to stronger fire, to be able to predict full-scale fire performance, but they might provide better guidance for research and development than the LOI [57].

The development of a fire in the flame spread and sustained burning stages is dependent upon the rate of heat release and is not inherently related to the total heat that would be released if the specimen burned to completion. An important aspect of the flame spread and sustained burning stages is the production of smoke and toxic gases. These stages, culminating in flashover when the fire is in an enclosure, are dominant as far as life safety is concerned. The important aspect of the third stage is fire endurance, in which efforts to contain the fire and save the structure depend in part upon the rate of combustion or rate of heat release of building contents and materials of construction. Test methods to evaluate the performance of building materials for flame spread, smoke production, and fire endurance have assumed major importance in efforts to control fires. The rate of heat release is a relatively new criterion for evaluating fire behavior and is expected to assume similar importance in research, material assessment, and building regulations.

Cone Calorimetry is a reliable technique that involves the determination of one specific physical, chemical, or behavioral characteristic of a material, product, or system. A system test would characterize the overall behavioral reaction of a material, product, or system with the environmental as well as internal variables which influence its performance. A system test involves interactions between the material, product, or system with its surroundings. Heat release rate test methods are among those classified as system tests. Cone Calorimeter predicts real-scale fire behavior of materials. The obtained results are used in the ranking of products for fire performance and assist in the development of new fire-resistant materials and products [58]. The physical observations that can be visualized during the tests are surface rising, deformation owing to intumescences, residual stresses, the collapse of structures, char cracking, char development and cracking through bubbling and sparking, creation of solid crusts, tiny explosions, surface layers or bubbles, afterglow, and so on. Cone Calorimeter has been used widely for a variety of samples including ornamental plants [59], wood [40], textiles [28] and polyvinyl chloride products [48, 60]. Moisture content, physical properties and chemical composition are all variables that impact the flammability of live plants and can be analyzed with the help of Cone Calorimeter.

#### **6. Conclusions**

Polymeric materials are normally compounded with various compounds to enhance their properties such as tensile strength, flexibility, stability and fire resistance to be used in specified applications. These properties are analyzed using efficient analytical techniques to rank the polymeric materials. Fire resistance property is analyzed with the help of Underwriters Laboratories Test standard UL-94, LOI test, Thermal Gravimetric analysis and Cone calorimetry. Underwriters Laboratories Test is specially designed for the evaluation of those plastic materials that used in appliances, in response to a small, open flame or radiant heat source under controlled laboratory conditions and it cannot be used for polymeric materials used in construction, wall and floor coverings or other decorative objects. LOI test results are only valid for specified conditions indicated in the test procedure and cannot be applied to real scale conditions. Thermogravimetric analysis predicts the volatile components evolved during the decomposition of the polymeric sample along with decomposition temperature; however, the fire characteristics of the polymer can be studied with the help of Cone calorimetric analysis. Cone calorimetry is a key tool for the real scale analysis of fire-resistant polymers. The flame profile data suggests the fire hazards and is important for development of new fire-resistant materials.

*Cone Calorimetry in Fire-Resistant Materials DOI: http://dx.doi.org/10.5772/intechopen.101976*

#### **Conflict of interest**

The authors declare no conflict of interest.

### **Author details**

Rakesh Kumar Soni\*, Meenu Teotia and Aakansha Sharma Department of Chemistry, Chaudhary Charan Singh University, Meerut, India

\*Address all correspondence to: rksoni\_rks@yahoo.com

© 2022 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

### **References**

[1] Bourbigot S, Le BM, Troitzsch J. Introduction. In: Troitzsch J, editor. Flammability Handbook. Munich: Hanser Verlag Publication; 2003. pp. 3-7

[2] Beard A, Angeler D. Flame retardants: Chemistry, applications, and environmental impacts. In: Handbook of Combustion. Weinheim: Wiley-VCH Verlag GmbH & Co. KGaA; 2010. DOI: 10.1002/9783527628148.hoc017. ISBN: 978-3-527-33449-1

[3] Lu SY, Hamerton I. Recent developments in the chemistry of halogen-free flame retardant polymers. Progress in Polymer Science. 2002;**27**(8): 1661-1712. DOI: 10.1016/S0079-6700 (02)00018-7

[4] Rahman F, Langford KH, Scrimshaw MD, Lester JN. Polybrominated diphenyl ether (PBDE) flame retardants. Sci Total Environ. 2001;**275**(1-3):1-17. DOI: 10.1016/ S0048-9697(01)00852-X

[5] Marosi G, Márton A, Anna P, Bertalan G, Marosföi B, Szép A. Ceramic precursor in flame retardant systems. In: Polymer Degradation and Stability. Vol. 77. Hungary: Elsevier; 2002. pp. 259-265. DOI: 10.1016/ S0141-3910(02)00057-5

[6] Chen L, Wang YZ. A review on flame retardant technology in China. Part I: Development of flame retardants. Polymers for Advanced Technologies. 2010;**21**(1):1-26 https://onlinelibrary. wiley.com/doi/full/10.1002/pat.1550

[7] Bourbigot S, Duquesne S. Fire retardant polymers: Recent developments and opportunities. Journal of Materials Chemistry. 2007;**17**(22): 2283-2300 https://pubs.rsc.org/en/ content/articlehtml/2007/jm/b702511d

[8] Kashiwagi T. Polymer combustion and flammability—Role of the condensed phase. Symposium on Combustion. 1994;**25**(1):1423-1437

[9] Staggs JEJ. Heat and mass transport in developing chars. Polymer Degradation and Stability. 2003;**82**(2):297-307

[10] Chen C, Yao B, Fan W, Liao G. A comparative experimental study on heat release rates of charring and noncharring solid combustible materials. Journal of Fire Sciences. 2016;**21**(5):369-382 https://journals.sagepub.com/doi/abs/ 10.1177/0734904103036091

[11] Boryniec S, Przygocki W. Polymer combustion processes. 3. Flame retardants for polymeric materials. Prog Rubber Plast Technol. 2001;**17**(2): 127-148 https://journals.sagepub.com/ doi/abs/10.1177/147776060101700204

[12] Levchik SV, Weil ED. Overview of the recent literature on flame retardancy and smoke suppression in PVC. Polymers for Advanced Technologies. 2005;**16**(10):707-716 https://onlinelibra ry.wiley.com/doi/full/10.1002/pat.645

[13] De Schryver D, Landry SD, Reed JS. Latest developments on the flame retardancy of engineering thermoplastics – SAYTEX® HP-7010 (brominated polystyrene) in glass filled engineering thermoplastics. Polymer Degradation and Stability. 1999;**64**(3): 471-477

[14] Iqbal A. Studying the Synergistic Effect of Aluminium Trihydroxide, Polyaniline and Other Fillers on EPDM Rubber. Lahore: Department of Chemical Engineering, COMSATS University; 2021 http://repository. cuilahore.edu.pk/xmlui/handle/ 123456789/2104

*Cone Calorimetry in Fire-Resistant Materials DOI: http://dx.doi.org/10.5772/intechopen.101976*

[15] Bosica R, Carosio F. Lignin-Based Nanocomposites with Fire-Retardancy Properties: Analysis and Implementation of an Innovative Material. KTH Royal Institute of Technology (SVEZIA): Politecnico di Torino; 2020. https://web thesis.biblio.polito.it/secure/cgi/set\_lang? lang=it&referrer=https%3A%2F%2Fweb thesis.biblio.polito.it%2F15625%2F

[16] Yang C, Jílková SR, Melymuk L, Harris SA, Jantunen LM, Pertili J, et al. Are we exposed to halogenated flame retardants from both primary and secondary sources? Environmental Science & Technology Letters. 2020; **7**(8):585-593. DOI: 10.1021/acs. estlett.0c00268

[17] Wang Y, Zhang F, Chen X, Jin Y, Zhang J. Burning and dripping behaviors of polymers under the UL94 vertical burning test conditions. Fire and Materials. 2010;**34**(4):203-215 https:// onlinelibrary.wiley.com/doi/full/ 10.1002/fam.1021

[18] Koncar V. Smart Textiles for In Situ Monitoring of Composites. The Textile Institute Book Series Elsevier: Woodhead Publishing; 2018. pp. 1-151. ISBN: 9780081023099

[19] Bajaj P, Jha NK, Maurya PL, Misra AC. Flame retardation of polypropylene: Effect of organoantimony compounds on the structural and mechanical properties. Journal of Applied Polymer Science. 1987;**34**(5):1785-1801 https://onlinelibra ry.wiley.com/doi/full/10.1002/a pp.1987.070340502

[20] Oxygen Index ASTM D2863. https:// www.intertek.com/polymers/testloped ia/oxygen-index-astm-d2863/

[21] Sidebotham GW, Cross JA, Wolf GL. A test method for measuring the minimum oxygen concentration to

support an intraluminal flame. ASTM Special Technical Publication. 1993;**1197**: 43-53 http://www.astm.org/DIGITAL\_ LIBRARY/STP/PAGES/STP24847S.htm

[22] Coats AW, Redfern JP. Thermogravimetric analysis. A review. The Analyst. 1963;**88**(1053):906-924 https://pubs.rsc.org/en/content/ articlehtml/1963/an/an9638800906

[23] Sakho EHM, Allahyari E, Oluwafemi OS, Thomas S, Kalarikkal N. Dynamic light scattering (DLS). In: Thomas S, Thomas R, Zachariah AK, Kumar R, editors. Thermal and Rheological Measurement Techniques for Nanomaterials Characterization. Cambridge, United states: Elsevier; May 23, 2017. pp. 37-49

[24] Ureyen ME, Kaynak E. Effect of zinc borate on flammability of pet woven fabrics. Advances in Polymer Technology. 2019;**22**:1-13

[25] Van Krevelen DW. Some basic aspects of flame resistance of polymeric materials. Polymer. 1975;**16**(8):615-620

[26] Stauffer É, Lentini JJ. ASTM standards for fire debris analysis: A review. Forensic Science International. 2003;**132**(1):63-67

[27] Weil ED, Patel NG, Said MM, Hirschler MM, Shakir S. Oxygen index: Correlations to other fire tests. Fire and Materials. 1992;**16**(4):159-167 https:// onlinelibrary.wiley.com/doi/full/ 10.1002/fam.810160402

[28] Schartel B, Hull TR. Development of fire-retarded materials—Interpretation of cone calorimeter data. Fire and Materials. 2007;**31**(5):327-354 https://onlinelibrary. wiley.com/doi/full/10.1002/fam.949

[29] Walters RN, Lyon RE. Molar group contributions to polymer flammability. Journal of Applied Polymer Science.

2003;**87**(3):548-563 https://onlinelibrary. wiley.com/doi/full/10.1002/app.11466

[30] Babrauskas V, Grayson SJ, editors. Heat Release in Fires. London,UK: Taylor & Francis; 1990

[31] Hirschler MM, Hoffmann DJ, Hoffmann JM, Kroll EC. Rate of heat release of plastic materials from car interiors. In: Proceedings of the 11th Annual Conference on Recent Advances in Flame Retardancy of Polymeric Materials. 2002. pp. 3-5 http://gbhint. tripod.com/papers\_5\_13\_02/378\_Cars\_ BCC2002.PDF

[32] Gann RG. Estimating data for incapacitation of people by fire smoke. Fire Technology. 2004;**40**(2):201-207 h ttps://link.springer.com/article/10.1023/ B:FIRE.0000016843.38848.37

[33] Fei Y, Jianjun Z, Yanghui Z, Peide L, Lin JZ, Chow TT. Preliminary real-scale experimental studies on cable fires in plenum. Journal of Fire Sciences. 2016; **21**(6):465-484

[34] Neviaser JL, Gann RG. Evaluation of toxic potency values for smoke from products and materials. Fire Technology. 2004;**40**(2):177-199 https://link.springe r.com/article/10.1023/B: FIRE.0000016842.67144.12

[35] Peacock RD, Averill JD, Reneke PA, Jones WW. Characteristics of fire scenarios in which sublethal effects of smoke are important. Fire Technology. 2004;**40**(2):127-147 https://link. springer.com/article/10.1023/B: FIRE.0000016840.14947.61

[36] Zacharoff H. Simulating Cable Fires in Fire Dynamics Simulator: Based on Small Scale Testing in Cone Calorimeter. Bachelor Thesis X7007B 15 ECTS: Department of Civil, Environmental and Natural Resources Engineering Lulea

University of Technology; 2021. http:// urn.kb.se/resolve?urn=urn:nbn:se:ltu:d iva-85995

[37] Twilley WH, Babrauskas V. User's Guide for the Cone Calorimeter. STIN: NASA STI/ Recon Technical Report N; 1988. Vol. 89 https://ui.adsabs.harvard. edu/abs/1988STIN...8922086T/abstract

[38] Nscort A. Estimation of Rate of Heat Release by Means of Oxygen Consumption Measurements. Intern Doc. Purdue University e-pubs: ALS-NCORT; 2003. https://docs.lib.purdue.edu/ alsinternal/303

[39] https://en.wikipedia.org/wiki/ Cone\_calorimeter

[40] Yang X, Zhang W. Flame Retardancy of wood-polymeric composites. In: Polymer-Based Multifunctional Nanocomposites and Their Applications. 2019 Higher Education Press: Elsevier Inc; 2019. pp. 285-317

[41] Babrauskas V. Development of the cone calorimeter—A bench-scale heat release rate apparatus based on oxygen consumption. Fire and Materials. 1984;**8**(2):81-95 https://onlinelibrary. wiley.com/doi/full/10.1002/fa m.810080206

[42] Lindholm J, Brink A, Hupa M. Cone Calorimeter—A Tool for Measuring Heat Release Rate. Turku, Finland: Åbo Akademi Process Chemistry Centre; 2009 http://ffrc.fi/FlameDays\_2009/4B/ LindholmPaper.pdf

[43] Janssens ML. Handbook of Environmental Degradation of Materials. 2nd ed. Elsevier, William Andrew; 2012

[44] Huggett C. Estimation of rate of heat release by means of oxygen consumption measurements. Fire and Materials. 1980; **4**(2):61-65. ISBN: 9781437734560

*Cone Calorimetry in Fire-Resistant Materials DOI: http://dx.doi.org/10.5772/intechopen.101976*

[45] Holdsworth AF, Horrocks AR, Kandola BK, Price D. The potential of metal oxalates as novel flame retardants and synergists for engineering polymers. Polymer degradation and stability. 2014; **110**:290-297

[46] Holdsworth AF, Horrocks AR, Kandola BK. Synthesis and thermal analytical screening of metal complexes as potential novel fire retardants in polyamide 6.6. Polymer Degradation and Stability. 2017;**144**:420-433

[47] Ramgobin A, Fontaine G, Penverne C, Bourbigot S. Thermal stability and fire properties of salen and metallosalens as fire retardants in thermoplastic polyurethane (TPU). Materials. 2017;**10**(6):665

[48] Teotia M, Verma A, Akitsu T, Tanaka S, Takahashi K, Soni RK. TGA decomposition and flame profile measurement of Terephthalamide stabilized PVC by cone calorimeter. Journal of Scientific and Industrial Research. 2017;**76**:438-441

[49] Schaffer EL. Review of Information Related to the Charring Rate of Wood. Vol. 145. United States Department of Agriculture, Research Note FPL-0145: Forest Products Laboratory; 1966

[50] JD ML. Thermal conductivity of wood. In: Heating, Piping and Air Conditioning. USA: Ashve Journal Section; Vol. 13. 1941. pp. 380-391

[51] https://nvlpubs.nist.gov/nistpubs/ Legacy/IR/nbsir82-2597

[52] Sonnier R, Vahabi H, Chivas-Joly C. New insights into the investigation of smoke production using a cone calorimeter. Fire Technology. 2019; **55**(3):853-873

[53] Östman BA, Tsantaridis LD. Correlation between cone calorimeter data and time to flashover in the room fire test. Fire and Materials. 1994;**18**(4): 205-209 https://onlinelibrary.wiley.com/ doi/full/10.1002/fam.810180403

[54] Hansen AS, Hovde PJ. Prediction of time to flashover in the ISO 9705 room corner test based on cone calorimeter test results. Fire and Materials. 2002; **26**(2):77-86 https://onlinelibrary.wiley. com/doi/full/10.1002/fam.788

[55] Petrella RV. The assessment of fullscale fire hazards from cone calorimeter data. Journal of Fire Sciences. 1994;**12**(1): 14-43 https://journals.sagepub.com/doi/ abs/10.1177/073490419401200102? journalCode=jfse

[56] Xu Q, Jin C, Zachar M, Majlingova A. Test flammability of PVC Wall panel with cone calorimetry. Procedia Eng. 2013;**62**:754-759

[57] Schartel B, Braun U. Comprehensive fire behaviour assessment of polymeric materials based on cone calorimeter investigations. E-Polymers. 2003;**3**(1):1-14

[58] An W, Jiang L, Sun J, Liew KM. Correlation analysis of sample thickness, heat flux, and cone calorimetry test data of polystyrene foam. Journal of Thermal Analysis and Calorimetry. 2014;**119**(1): 229-238 https://link.springer.com/ article/10.1007/s10973-014-4165-9

[59] Weise DR, White RH, Beall FC, Etlinger M. Use of the cone calorimeter to detect seasonal differences in selected combustion characteristics of ornamental vegetation\*. Int J Wildl Fire. 2005;**14**(3):321-338 https://www. publish.csiro.au/wf/WF04035

[60] Soni RK, Sharma A, TAkitsu, T. and Teotia, M. Flame profile measurement of Cu (II) based Salen complex filled thermally stabilized PVC sheets by cone calorimeter. Journal of Scientific and Industrial Research. 2020;**79**(7):582-585

Section 3
